For many years, aircraft have included as standard equipment backup power supplied for use in times of power outage in the form of air driven turbines or fans which are lowered into the airstream, thereby making use of the relative speed of the aircraft through the ambient air to cause the turbine blades or propellers to rotate. The rotation imparted to the blades due to their movement through the air is then used to drive electrical generating gear or provide hydraulic power to the aircraft hydraulic system during the aforementioned times of power outages. These air driven propeller arrangements conventionally include governor mechanisms that attempt to control the output rotational speed delivered from the propellers to electrical or hydraulic units that are designed to operate most efficiently at a set or given speed.
Typical of the best efforts of the past is that of Blackburn as evidenced by U.S. Pat. No. 3,013,613 ('613) and Blackburn et al, U.S. Pat. No. 2,876,847 ('847).
Blackburn ('613) depicts an arrangement where the governor control mechanism has, as best seen, in FIG. 1 and FIG. 3, governor flyweights 64 which are connected via a pair of pins 74, 78 and link 76, respectively, to the flyweight 67 and a slider assembly 42. The slider assembly 42, in turn, has a pair of pins 80 which are connected to the inner ends of links 82, the outer ends of links 82 being rotatably connected to crank pins 84. The cranks pins 84 are carried by crank arms 86 which are drivingly connected with a stub shaft 60, which stub shaft is secured to the blade, the pitch of which is to be controlled. Auxiliary counterweights 70 are also rigidly attached to each stub shaft 60. The invention to be described more fully, hereinafter, does away with virtually all of the pins and linkages required in Blackburn ('613), which results in an inherently more efficient device for controlling blade pitch in response to blade speed.
Blackburn et al ('847) holds special interest because this patent puts forth the idea of providing coarse or high pitch blade positioning for the propeller involved when the entire unit is stationary or in storage. Blackburn et al ('847) accomplishes coarse pitch positioning of a blade or propeller 31 by incorporating a coiled extension spring 56 which is wound around the root of the propeller blade and secured to pins 55, 63 such that, when the unit is stationary the coiled extension spring 56 will contract and rotate the blades 31 to a high or coarse pitch position. The invention to be described hereinafter, does away with need to bend a coiled extension spring, but relies on the direct transmission of the stored energy in a compressed spring which energy is delivered in a straight line fashion to and through a pin and yoke arrangement to the blade to be controlled.